duttomJ THE CRETACEOUS OF THE TERRACES. 75 



scarps which terminate the summits of the Markagunt and Paunsagunt 

 Plateaus. Their color varies with the light and atmosphere. It is a 

 pale red under ordinary lights, but as the sun sinks towards the horizon 

 it deepens into a rich rose color, which is seen in no other rocks and is 

 beautiful beyond description. These cliffs are of lower Eocene age, con- 

 sisting of lake marls very uniformly bedded. At the base of this series 

 the beds are coarser, and contain well-marked, brackish-water fossils; 

 but as we ascend to the higher beds we find the great mass of the Eocene 

 to consist of fresh-water deposits. 



These beds are identical in age with the lower divisions of the Eocene 

 which are seen in great volume both north and south of the Uinta 

 Mountains, in the basins of the Green River, of Bitter Creek, and of the 

 White and Uinta Rivers. Their geological relations and associations, too, 

 are quite the same, for the same lake bottom received the deposits of the 

 southern Uinta slopes and those of the Markagunt. Those of the Green 

 River basin north of the Uintas appear to have accumulated in a sepa- 

 rate lake basin communicating with the one which submerged the south 

 ern Plateau province. The interval separating the Markagunt from 

 the Uinta region is 250 miles and more, but the lower Eocene is contin- 

 uous between them. It occupies a marginal belt sometimes narrow, 

 but more frequently wide, which was once the locus of the northwestern 

 portion and shore line of the great lake. The summits of the High Pla- 

 teaus, wherever the volcanic masses are absent, disclose this formation, 

 and its presence is decisively inferred beneath the lavas and their debris. 

 A common bond between the two regions is also indicated by the 

 physical conditions attending the deposition of these strata. The lower 

 Eocene rests upon the underlying formations, conformably in some places, 

 iinconformably in others. Where conformity prevails, both the upper 

 and lower series were at the time of deposition sensibly horizontal. 

 Rutin many places the Cretaceous, prior to the deposition of the Eocene, 

 was greatly disturbed and greatly eroded. And in general the base of 

 the Eocene marks an epoch in the geological history of the country, in 

 which an old order of events was closing and a new order was making 

 its advent. This revolution was the transition of the region from the 

 oceanic condition to that of an estuary and lake, and subsequently to that 

 of dry land. The Lower Eocene beds are brackish-water deposits in 

 the basal members, while higher up they become fresh water. The 

 basal memhers are coarse and even conglomeratic in their texture, while 

 the middle and higher ones are fine and marly. Thus is indicated the 

 complete severence of the lake from the access of oceanic waters. Both 

 in the Uinta district and throughout the High Plateaus these events 

 are recorded in the same order and their meaning is the same in both. 



The beds now found in the southern extremities of the High Pla- 

 teaus represent less than half of the duration of Eocene time. No 

 middle and no upper Eocene strata are found there. But as we go 

 northward towards the Uintas we find later and later formations sue- 



